Method and device for waking users of a bus system and corresponding users

ABSTRACT

An apparatus for waking up users of a CAN bus system, wherein a sensing element, in particular a counter, is provided which senses at least one predefined signal property of the signals transmitted on the bus system and initiates the further wakeup operation when a predefined number is reached with reference to the signal property, the data stream of the CAN bus itself being used as a clock for detecting the signal property.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for waking upusers of a bus system, and a corresponding user.

BACKGROUND INFORMATION

Control devices in motor vehicles are, to an increasing extent,continuously supplied with voltage (also called “terminal 30”capability) so that certain monitoring and control functions can beperformed even with the ignition switched off. These can be instancesof, for example, access and driving authorization, or diagnosis. Toreduce power consumption, the control devices are put into a so-called“sleep” mode. This is done either by switching off the voltage regulatoror by entering into a corresponding operating mode of themicrocontroller.

The control device must be woken up when necessary. This occurs by wayof a lead, provided for the purpose, either to a wakeup input of themicrocontroller of the user or to a wakeup input of the voltageregulator. In present-day systems, which are usually networked, it canalso occur by way of an activity on the bus lines.

A disadvantage of this is that either a separate wakeup lead must berouted to all required control devices; or in the case of waking via thebus, all the control devices (including those not required) are woken bya desired or undesired bus activity, either by communication on the busor by interference on the bus.

Present-day CAN transceivers can be operated substantially in two modes:in the active mode for communication, and in the sleep mode for thepower-saving idle state. The application program can set the desiredoperating mode; the transceiver also switches, in particularautomatically, from the sleep mode into the active mode as soon as itdetects a signal or a signal property, e.g., a dominant bit, on the CANbus. While the transceiver is in sleep mode, the remainder of the CANnode can be switched off and is then switched back on when the CANtransceiver switches into the active mode.

German Patent Application No. DE 103 58 584 A1 describes a method bywhich a CAN transceiver is expanded to include a circuit that decodes8-bit-long patterns from an 8-byte-long data field of a CAN message. Asa result, the CAN transceiver can be operated in four modes. In additionto the modes previously described, there is also a further economy modeand an intermediate mode. The transceiver automatically switches fromthe sleep mode into the economy mode as soon as it detects a dominantbit on the CAN bus. In the economy mode, it senses a signal property andswitches into the intermediate mode when it detects a number of signalproperties, for example edges, within a predefined time span. It thenswitches from the intermediate mode into the active mode only as soon asit detects a specific pattern in the 8-byte-long data field of there-transmitted CAN message, which it decodes for that purpose accordingto a specific method. This wakeup pattern can be configured separatelyfor each CAN transceiver. The CAN identifier of this message ispredefined for this method. If it does not detect the wakeup pattern inthis message, it goes back into economy mode. The power consumption inthe intermediate mode is only slightly higher than in the economy mode;the remainder of the CAN node can remain switched off. This makespossible CAN networks in which individual nodes remain in controlledfashion in the power-saving economy mode, while the other nodescommunicate via the CAN bus. The individual nodes can be selectivelywoken up from the economy mode. This is also called “selective wakeup.”

It is thus possible, via the bus used in motor vehicles (in particular aCAN bus), to selectively wake up only the control devices that areneeded in order to perform the necessary functions.

SUMMARY

An object of the present invention is to provide a method and anapparatus that expand the selective wakeup method so that differentidentifiers for the wakeup message can also be programmed.

In accordance with the present invention, a method and an apparatus forwaking up users of a bus system are provided, a counter being providedwhich counts at least one predefined signal property of the signalstransferred on the bus system, and initiates the further wakeupoperation upon reaching a predefined number.

Advantageously, an edge or an edge transition of the signal is providedas a predefined signal property.

A signal level or a specific combination of several signal levels canlikewise usefully be provided as a predefined signal property.

It is particularly advantageous if upon the first occurrence of thesignal property, a time duration is determined; and there results fromthe time duration thereby determined, after the first occurrence, fromthe signal properties referred to the time duration, a binaryinformation that enables a selective wakeup of users of the bus system.

The user to be woken up can be read out from the information obtained;this can be accomplished by analysis of the bulletin or message that hasled to authorization of the sleep mode, or also of a re-transmittedfurther wakeup bulletin or message.

Advantageously, the control devices connected to the bus can thusentirely switch off their microcontrollers, or put them into a sleepmode having clocks likewise switched off, such that only the transceiverconnected to the bus, in particular a CAN transceiver of very low powerconsumption, needs to be supplied with standby power. Thanks to the useof the time duration that is determined upon the first occurrence of oneof the signal properties, decoding can occur irrespective of the bussystem transfer rate that is used, and errors in the block structurewith respect to the communication blocks in the bus system canadditionally be detected by way of the evaluation.

The configuration capabilities for the wakeup method via the CANtransceiver having a selective wakeup function are expanded, accordingto the present invention, to include a setting as to how many edges areto be counted in the arbitration field and the control field of thewakeup message. Each message for which this count yields the presetvalue is regarded provisionally as a wakeup message (first stage of themethod), pending successful decoding of the wakeup pattern encodedaccording to a specific method in the data field (second stage of themethod).

An advantage of this method is that in the configuration of the CANnetwork, the identifier for the wakeup message can be freely selected,for example in terms of its priority by comparison with the othermessages. Both an 11-bit identifier and a 29-bit identifier can beselected. Various CAN nodes in the network can also use different wakeupidentifiers, thereby increasing the number of nodes that can beindividually woken up.

A further advantage of the method is that the clock of the transceivercan be switched off before the wakeup operation begins, since the bussignal that is present is itself employed as a clock for the first stageof the wakeup method.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in further detail with reference tothe Figures.

FIG. 1 shows a bus system having several, at least two, users.

FIG. 2 shows an example method sequence according to the presentinvention in the form of a flow chart.

FIG. 3 depicts, by way of example, a bulletin having the wakeupinformation encoded in the data field.

FIG. 4 shows the example structure according to the present invention ofa block in the data field for identifying the signal property havingencoded information.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows a bus system 100 having bus users 101, 102, and 103. Thelatter each contain a transceiver or a media connector unit 107, 108,109 respectively, as well as a time-sensing or counting module having anintegrated clock 104, 105, or 106. The latter can in each case belocated outside the corresponding transceiver or media connector unit,but can also be expressed as a constituent thereof. As alreadymentioned, in this exemplifying embodiment only those control devicesthat are needed to perform the required functions are to be selectivelywoken via the CAN bus that is often used in motor vehicles. Devices canalso be combined into groups that react to the same wakeup information.

One possibility would be to use specific parts of a message or of a CANframe (e.g., identifier) for selection. A prerequisite for this,however, is that the wakeup device be continuously connected to a clockthat is in operation; this, however, makes a substantial contribution topower consumption. This kind of wakeup requires that the transfer rateof the bus be known, and that the clock must exhibit only very smallfluctuations as a result of external influences such as, for example,supply voltage or temperature, etc. A selection method operates inmultiple stages, and that in the first stage makes do without clocksthat are in operation.

In the idle state, the control devices or users that are connected tothe bus, for example 102 and 103, can switch off their microcontrollerscompletely or put them into a state with a switched-off clock. Thetime-sensing or counting module having clock 105 or 106, respectively,is also put into a sleep mode in which the integrated clock is switchedoff. In the users in the idle state, for example 102 and 103, only theCAN transceiver connected to the bus, or the media connector unit,having a very low power consumption, is supplied with standby power.

The selection mechanism becomes activated when a user, for example 101,transmits on the bus a characteristic signal for waking up users 102and/or 103. In a first step, users 102 and 103 switch into the economymode and count edges of the transmitted bus signal. The time-sensing orcounting module having clock 105 or 106 becomes activated. Theswitchover into the intermediate state occurs as a function of theresult of the edge count. In the intermediate state, the content of thedata field is decoded with the aid of clock 105 or 106, and is comparedwith a stored wakeup address. In the event of a positive result, theuser switches into the active mode and, for example, themicrocontrollers and/or further voltage regulators of users 102 and 103,respectively, become activated.

The present invention can similarly be implemented as a single-stagewakeup in which both steps of the method are cycled through based on theevaluation of a single received message. It is also possible, however,in order to further enhance wakeup reliability, to execute a two-stagewakeup in which the two steps of the method are cycled through based onthe evaluation of two successively received messages.

If multiple devices react to the same wakeup mechanisms (to the samecharacteristic signals), then entire groups of devices can also bewoken; or the devices can be combined into groups, or specific devicescan be woken for specific applications.

By way of the logical structure, it is possible to derive theinformation from the message irrespective of the transfer rate used, aswill be explained in further detail later on. In this context, thenumber of changes between High and Low, or 0 and 1, i.e., the binaryinformation, is largely constant.

It is particularly preferred that the wakeup message be a bulletin thatis constructed according to the CAN bus ISO standard, that does notviolate said standard and thus causes no problems in existing systems. ACAN controller, as used in other approaches, is then not necessary here.

The configuration capabilities for the wakeup method via the CANtransceiver having a selective wakeup function are expanded, accordingto the present invention, to include a setting as to how many edges areto be counted in the arbitration field and control field of the wakeupmessage. Every message for which this count yields the preset value isregarded provisionally as a wakeup message (first stage of the method),pending successful decoding of the wakeup pattern encoded, according themethod described below, in the data field (second stage of the method).

In the configuration of the CAN network, the identifier for the wakeupmessage can be freely selected, for example with regard to its priorityas compared with the other messages. Both an 11-bit identifier and a29-bit identifier can be selected. Various CAN nodes in the network canalso use different wakeup identifiers, thereby increasing the number ofnodes that can be individually woken up. If only the arbitration fieldand control field are evaluated (as in this example), the result of thefirst stage of the wakeup method is available in time for the secondstage, i.e. decoding of the wakeup pattern in the data field, still tobe carried out on the basis of the same message.

FIG. 2 depicts a schematic flow chart as an example. FIG. 3 depicts, byway of example, the format of the wakeup message and the two steps ofthe wakeup procedure. The sender of the wakeup request sends on the bus,such as a CAN bus in the example here, a message A in accordance withFIG. 3, in which message the receiver or receiver group to be woken upis encoded with a number. In the idle state, the bus is recessive. Whenthe first bulletin comes (which can be detected by the switchover todominant and occurs in block 1 of FIG. 2), a counter is activated. Thenumber of edges of the bulletin is then counted over a specific time,for example during the arbitration field and the control field, in block2 of FIG. 2. For synchronization to the bus clock cycle, the bit streamof the bus is evaluated in accordance with the method discussed below.

If the number of edges ascertained is within the permissible limits, thesecond part of the circuit is activated. A first separation is therebyachieved between communication or interference on the bus, and a wakeuprequest. If this comparison turns out positive, i.e., if a wakeuprequest exists, the second stage of the logic system is supplied withpower. The wakeup logic system, i.e., in particular the processing unit,reads out from the data field using time-sensing or counting module 105,106, in accordance with the example method discussed below, the numberof the device or device group that is to be woken up. This occurs inblock 3 of FIG. 2. If the number read out matches a stored one, thedevice is activated in block 4 of FIG. 2 by activating the voltageregulators or waking up the microcontroller, and the corresponding userparticipates in bus traffic. In this flow chart, the two-stage wakeupmethod is depicted with the combination of blocks 2 and 3, as describedabove. It is likewise possible to use only one of the two stages as awakeup criterion.

With five configuration bits, for example, the maximum possible numberof edges in the combined arbitration and control field of a CAN dataframe can be described with 29-bit identifiers and DLC-8. Optionally,all the edges can be counted, or only those from dominant to recessive,or those from recessive to dominant. The target value, or a permissiblerange, for the edges expected in a wakeup message can be stored in asuitable memory region, and used for the first step of the wakeupoperation.

Digital circuits that are intended to decode the patterns from serialdata sequences use a clock cycle for that purpose. An objective of theexample method described here is to minimize the power consumption ofthe transceiver for the time before it has detected the wakeup pattern.The clock cycle is therefore halted when it is not required fordecoding, and restarted as soon as the beginning of a message (dominantSOF bit) is detected.

The particular decoding method for the wakeup pattern in the data fieldof a CAN message allows a considerably higher clock cycle tolerance thanthe CAN protocol itself. An oscillator nevertheless needs time tostabilize adequately after it starts.

The clock cycle of the oscillator is therefore not used for counting theedges in the arbitration field and control field, but instead the datastream of the CAN bus itself is used as a clock cycle. This data streamcan be used serially. This is the first stage of the wakeup method. As aresult, the oscillator has at least 18 CAN bit times (36 is at 500kbit/s) to stabilize itself before an attempt is then made, in thesecond stage of the wakeup method, to decode the wakeup pattern usingthat clock cycle. For this, the CAN transceiver is switched into theintermediate mode.

This two-stage decoder method can, with a single CAN message, bring aCAN transceiver out of the economy mode into the active mode, and wakeup the remainder of the CAN node.

A variety of conditions can be defined as to when the oscillator of thetransceiver is stopped again:

-   1. The transceiver switches into the active mode.-   2. The edge counter reaches a specific value. This value is    determined from the configured value of the edges in the arbitration    and control field plus a constant, since the particular form of the    wakeup pattern coding stipulates a constant number of edges in a    valid wakeup pattern.-   3. A time circuit (e.g. RC element) starting at an SOF bit.-   4. The CAN bus remains at the recessive level for more than    approximately six CAN bit times (measured with e.g. an RC element).

FIG. 3 shows the procedure in the second stage of the wakeup method.According to FIG. 3, message A is used in a preferred form as a messageconstructed according to the CAN bus ISO standard. A “start of frame”(SOF), an arbitration field that as a rule contains the identifier, anda control field are provided before the data field. Contained after thedata field is a check number as a cyclic redundancy check (CRC), and aconfirmation field with regard to the bulletin transfer (anacknowledgment ACK). Message A contains the number of the device ordevice group in the data field. Any valid CAN address can be used as aCAN identifier. The frame thus conforms to the CAN bus specification,and communication by other devices via the CAN bus is not disrupted.

As depicted in FIG. 3, the entire data field in the frame, in particularin the CAN frame, is made up here of 64 bits subdivided into eightblocks, i.e., block 0 to block 7. At least one bit of the device numberis encoded in each block. If exactly one bit of the device number isencoded in each block, the circuit can obtain, from a CAN frame asdepicted, eight bits for further processing. Transfer errors can bedetected by way of the interleaving of these eight bits.

The particular structure of the individual blocks 0 to 7 of FIG. 3 isdepicted in FIG. 4. As a result of this particular structure of theeight blocks, coding can occur irrespective of the bus transfer ratethat is used. In addition, errors in the block structure can still bedetected. In this context, one block corresponds to eight bits from theCAN data field.

The structure of a block is depicted by way of example in FIG. 4. Herebits 2 and 3 are High in order to measure or determine a time t. Afterthe end of bit 3, the wakeup logic or processing unit waits once for thepreviously determined time t and stores the state that then occurs, thenwaits for time t once again and stores the new state that then occurs.The times t and 2 t as depicted in FIG. 4 can be selected so that Highor Low signals can be entirely detected in the context of the signallevels. Also possible is a detection of the signal edges, for examplefrom bit 4 to bit 5 and bit 6 to bit 7, by corresponding selection ofthe respective time segments. What results is a coding capability,irrespective of the transfer rate used, for a 0 information (here inbits 5 and 6) and a 1 information (here via bits 7 and 8).

In other words, in the coding example in FIG. 4, bit 1 is always 0 andbit 2 and bit 3 are always 1, in order to calibrate time t; and bit 4 isin turn always 0 for separation between the calibration time and theactual binary information. Bits 5 and 6 are selected here so that theyare at High, which then means a logical 0 for the block. Bits 7 and 8are then selected in such a way, which would signify a logical 1 for theblock. In other words, if bits 5 and 6 are at 1, the block contains alogical 0; and if bits 7 and 8 are at 1, the block then contains alogical 1. In other words, the bits are set here so that either bits 5and 6 are at 1, or bits 7 and 8. In other words, the example methoddescribed here exhibits a baud-rate-independent transfer, in particularby counting edges or edge transitions, or the corresponding signallevel, in accordance with the respectively predefined signal property:on the one hand as a first wakeup stage and, in the context ofevaluation of the encoded binary information in the same message, as asecond, selective wakeup stage, in a multi-stage concept. The predefinedsignal property can be, as already mentioned, on the one hand the signallevel (i.e. 0 or 1 as in the example of FIG. 4) but also, as alreadystated, evaluation of the signal edges or of the signal edge transition.What results is a simple capability for selectively waking up controldevices without entailing additional circuit complexity and withoutalways producing power consumption by all the users of the bus system,including those that are not needed.

The CAN transceivers described here can be used for CAN and/or for TTCANnetworks.

What is claimed is:
 1. An apparatus for waking up users of a CAN bus system, comprising: a sensing element configured to sense at least one predefined signal property of a signal transmitted on the bus system and to initiate a further wakeup operation when a predefined number is reached with reference to the signal property; wherein a data stream of the CAN bus itself is used as a clock cycle for detecting the at least one predefined signal property, and wherein the at least one predefined signal property is a specified number of edges in at least one of an arbitration field and a control field of a CAN message.
 2. The apparatus as recited in claim 1, further comprising: a counter to count occurrences of one of the at least one signal property.
 3. The apparatus as recited in claim 1, wherein the predefined number at the reaching of which the further wakeup operation is initiated is stored in a memory region.
 4. The apparatus as recited in claim 1, further comprising: one of a counter or a timer to sense a time duration between two sensing times of signal properties.
 5. The apparatus as recited in claim 4, wherein the one of the counter or timer is switched off before the beginning of the wakeup operation.
 6. The apparatus as recited in claim 1, wherein for the further wakeup operation, at least one of: i) at least one profile, ii) at least one pattern, or iii) at least one sequence of at least one signal property is sensed, and is compared with at least one of: i) at least one profile, ii) at least one pattern, or iii) at least one sequence stored in a memory provided therefor.
 7. The method as recited in claim 6, wherein a time duration is determined upon occurrence of one of the at least one signal property.
 8. The method as recited in claim 7, further comprising: ascertaining binary information from a value of one of the at least one signal property after a previously ascertained time duration has elapsed again at least once; creating one of a profile, a sequence, or a pattern of signal property from several items of binary information ascertained; and comparing the one of the profile, the sequence, or the pattern of the signal property with one of: i) at least one stored profile, ii) at least one stored sequence, or iii) at least one stored pattern, wherein the wakeup operation is or is not initiated as a function of a result of the first comparison.
 9. The method as recited in claim 6, wherein in a first step, one of the at least one signal property is counted by a counter and is compared in a first comparison with at least one threshold value or limit value, and the wakeup operation is initiated as a function of the result of the first comparison; and in a second step, a time duration is ascertained from a value of one of the at least one signal property, and binary information is ascertained after the ascertained time duration has elapsed again at least once, wherein from several items of binary information ascertained, one of a profile, a sequence, or a pattern of a signal property is created and is compared with at least one of: i) at least one stored profile, ii) at least one stored sequence, or iii) at least one stored pattern, and the wakeup operation is or is not carried out as a function of a result of the second comparison.
 10. The method as recited in claim 9, wherein a message received in an idle state is evaluated as a wakeup message, the first step of the wakeup method and the second step, selective for one of individual users or groups of users, of the wakeup method being carried out by evaluating a same message that is received once.
 11. The method as recited in claim 9, wherein wakeup messages are sent several times, and a message received in an idle state is evaluated as a wakeup message, and after initiation of the further wakeup operation, another reception of the wakeup message is awaited, and after another reception, the second step, selective for individual users or groups of users, of the wakeup method is carried out.
 12. A method for waking up users of a CAN bus system, comprising: sensing at least one predefined signal property of a signal transmitted on the bus system; and initializing a further wakeup operation when a predefined number is reached with reference to the signal property; wherein a data stream of the CAN bus itself is used as a clock cycle for detecting the at least one predefined signal property, and wherein the at least one predefined signal property is a specified number of edges in at least one of an arbitration field and a control field of a CAN message.
 13. The method as recited in claim 12, further comprising: sending a message over the bus system; evaluating the message as a wakeup message by sensing; and evaluating at least one of the at least one signal property from the message.
 14. The method as recited in claim 13, wherein one of the at least one signal property is counted by a counter and is compared with at least one threshold value or limit value, and as a function of the result of the comparison, the wakeup operation is or is not initiated.
 15. A user of a CAN bus system, comprising: an apparatus for waking up users of the CAN bus system, the apparatus including a sensing element configured to sense at least one predefined signal property of a signal transmitted on the bus system and to initiate a further wakeup operation when a predefined number is reached with reference to the signal property, wherein a data stream of the CAN bus itself is used as a clock cycle for detecting the at least one predefined signal property, and wherein the at least one predefined signal property is a specified number of edges in at least one of an arbitration field and a control field of a CAN message. 